1. Field of the Invention
The present invention relates, in general, to automatic watthour meter reading apparatus and, specifically, to remote automatic watthour meter reading apparatus.
2. Description of the Art
The advantages of automatic reading of electrical watthour meters and other utility meters have long been recognized. Such advantages accrue from the elimination of the high costs associated with manually reading meters located a long distance from a central utility office, inside of a customer's premises, at dangerous locations, and at the remote ends of a distribution network. Further, in rural utility networks, long distances are typically encountered between each meter location. Thus, more employees are required to manually read each meter on a predetermined time schedule for accurate billing.
However, such advantages have not been fully attained by previously devised automatic meter reading apparatus for several reasons. Most automatic meter reading apparatus require a specially designed watthour meter containing the telephone communications circuit, the power measuring circuitry and the data accumulation circuitry. In a typical electrical utility having tens to hundreds of thousands of electrical meters, the capital cost of replacing all watthour meters with specially designed automatic reading watthour meters is extremely high. Further, a single utility system typically uses several different types of watthour meters. Converting such meters in all locations to automatic reading meters is impractical since it would require several different types of automatic meter reading apparatus thereby increasing inventory and complicating ordering, installation and service of the meters. Previously devised automatic meter reading apparatus have also had a high cost compared to conventional, single phase, mechanical rotating ring-type counter meters and have other disadvantages which have limited their widespread application.
In the context of providing an economical, easily installed, widely usable automatic meter reading apparatus for watthour meters, another factor which must be addressed is accuracy in measuring power usage. The accuracy standard for automatic meter reading apparatus is the .+-.2% accuracy of conventional mechanical watthour meters. Some automatic meter reading devices sense rotation of the mechanical rotating ring in a conventional watthour meter and convert the sensed rotations to digital signals corresponding to indicated power usage. Thus, such automatic meter reading devices are limited to the accuracy of the mechanical watthour meter. Electronic sensing of current and voltage for the calculation of power has also been proposed for electronic watthour meterrs. Such sensing circuits have been specifically designed for use in a specially designed electronic watthour meter. However, little attention has been paid in such single phase watthour meters for accurately measuring power consumption.
Another disadvantage of previously devised automatic meter reading devices utilizing conventional telephone lines has been the inclusion of complex telephone dialing, call-back and reporting circuits to coordinate the flow of power usage information between each remote watthour meter site and the central utility office. This has increased the cost of automatic meter reading devices beyond the point of widespread economical implementation. Further, the use of dedicated telephone lines which do not interfere with a customer's telephone usage has also been proposed along with the attendant cost of running additional telephone lines to each customer site.
Another factor which has not been fully addressed by previously devised automatic meter reading devices is the desirability of having time of day and demand power control by the utility company at residential locations. The increased cost of generating electricity has required other billing approaches by utilities including time of day billing where varying rates are applied to electrical usage at different periods during each 24 hour day. Another billing approach is demand or peak billing where the amount of power consumed is billed at a higher rate for power usage exceeding a predetermined amount. In order to implement such alternate billing approaches, it is necessary for the utility company to have accurate power consumption data, such as having the ability to determine the peak load of any customer and the power usage during any time period during the day.
Thus, it would be desirable to provide an automatic meter reading device for watthour meters which overcomes the problems of previously devised automatic meter reading devices. It would also be desirable to provide an automatic meter reading device which is usable with conventional watthour meters without requiring modifications to such watthour meters or the meter socket. It would also be desirable to provide an automatic meter reading device for watthour meters which utilizes data communication via conventional telephone lines with a central utility site. It would also be desirable to provide an automatic meter reading device for watthour meters which is usable with most of the many different types of watthour meters currently used by utility companies.